Electrically controlled rear vision mirrors are in common use, and usually incorporate a mechanism consisting of one or two miniature electric motors driving, via reduction gear systems, a mirror holder rotationally and separately through two axes disposed at 90.degree. to one another.
The motors usually drive the mirror holder through a gear system, the shaft of each motor having on it a gear drive worm which engages the teeth of a respective spur or helical gear over a segment of the diameter of the worm gear. The spur or helical gear usually comprises a nut having a co-axial screw thread which engages a non-rotational screw shaft connected pivotally to the mirror holder at a point radially displaced from the tilt axis of the mirror holder.
Motor vehicles frequently carry micro-processors having large memory banks which are not fully utilized, and have sufficient surplus capacity to control orientation of the mirrors, for example to occupy former positions suitable for a specific driver. This avoids the need for a driver to separately adjust each mirror each time he enters a vehicle, since he can effect the required adjustments by utilizing the memory bank facilities. However to achieve this it is necessary for there to be position sensing means within the mirror housing, and position sensing means usually involve potentiometers, which, in a mirror, would be coupled to the mirror housing directly or indirectly so as to sense the mirror position. They would transmit respective voltage signals to the micro-processor which would identify the mirror orientation with sufficient accuracy to be practicable. Such an arrangement would employ known principles.
However, a mirror housing is essentially a small housing, and it is inconvenient to use separately positioned potentiometers therein. Further, potentiometers add to the cost of the assembly. There are usually two electrically adjusted mirrors on a vehicle, and therefore it becomes necessary to have a total of four potentiometers.
The main object of this invention is to provide improvements whereby the costs can be reduced and yet whereby excellent potentiometer provisions are made without the need for additional devices to be included within a mirror housing.